Delayed appearance of decorin in healing burn scars

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Abstract
We have previously shown that hypertrophic scar tissue from burn patients contains abnormally high amounts of the proteoglycans versican and biglycan and reduced amounts of decorin, in comparison with normal dermis or mature scar. The lack of decorin may account for the poor organization of collagen fibrils in the nodular areas of these scars. Decorin has also been reported to neutralize the fibrogenic growth factor TGF-β1. This study was conducted to monitor the time-course of expression of decorin in healing burn wounds by in-situ hybridization to determine whether its absence from hypertrophic scars could result from reduced synthesis. Scar tissue from 19 patients and normal dermis from six patients, was fixed in paraformaldehyde, embedded in paraffin and sectioned. Digoxigenin-labelled cRNA probes were prepared from a plasmid containing a 622-bp insert of human decorin cDNA and used for in-situ hybridization. Total numbers of connective tissue cells and cells positive for decorin mRNA were counted in 10 random fields in the upper (papillary), middle and lower (reticular) one-thirds of the dermis. In all regions the number and percentages of cells with decorin mRNA were low during the first 12 months after injury (eight samples), much higher between 12 and 36 months (seven samples) and low and similar to those in normal skin after 36 months (five samples). The differences between intermediate and early or late stage samples were statistically significant (one-way anova). Immunohistochemistry showed little staining for decorin in early stage samples and much stronger staining in mid-stage. Late stage tissue showed intense staining for decorin, almost comparable to that in normal dermis. Expression of decorin in burn wounds is suppressed for about 12 months and then increases at a time when resolution of hypertrophic scarring is generally considered to occur.